Electroplating copper containing coating



Patented Mar. 1, 1949 ELECTROPLATING COPPER CONTAINING COATING George W. Kellogg Flint, Mich., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware No Drawing. Application February 21, 1942, Serial No. 431,823

1 Claim. 1

This invention has to do generally with improvements in electroplating practice and more specifically with the treatment of electrodeposited coatings of copper and a metal such as zinc or tin on metal surfaces in order to form corrosionresistant coatings.

It has been heretofore proposed to electrodeposit separate coatings of copper and zinc or separate coatings of copper and tin on a metal surface and thereafter heat treat the metal surface and separate coatings in an attempt to diffuse the metals of the two platings into one another and to form what is described as a coating of brass or bronze on the metal surface. It has also been proposed to electrodeposit simultaneously both copper and zinc to produce a brass plating and to simultaneously deposit copper and tin to produce a bronze plating. Platings produced by these prior art proposals fail rather rapidly when subjected to standard salt spray tests and/or are subject to other serious disadvantages.

The primary object of the present invention is to provide a convenient and practical method of producing a corrosion-resistant electrodeposited coating of copper and a metal such as zinc or tin having a lower melting point than copper, on a metal surface.

The method of the present invention broadly consists in simultaneously electrodepositing both copper and the metal such as zinc or tin onto a metal surface and thereafter heat treating the metal and electrodeposited coating thereon to elevated temperatures under such conditions that the corrosion-resistance of the coating is increased greatly, Preferably temperatures somewhat above the melting point of the low melting constituent, such as zinc or tin, are employed and, in any event, temperatures not much below the melting point of the zinc or tin. Preferably temperatures below the melting point of copper are used. The temperature in any case is below the melting point of the metal surface on which the electrodeposit is formed. The metal surface and coating are maintained at the elevated temperature for a time interval sufficient to result in a product having the desired corrosion-resistant coating thereon. The time will vary with the temperature and the composition of the electrodeposit. Preferably the heating is carried out under nonoxidizing conditions, although it appears that this is not essential in most applications of the invention.

The composition of the codeposit of copper and the low melting constituent such as zinc or tin may vary considerably. At present it is preferred that the codeposit consist of about copper and about 30% zinc where zinc is employed as the low melting metal. In general it is contemplated that the percentages of copper and zinc in the electrodeposited coating may vary within the limits of composition of known brasses containing these constituents. In the case of codeposits of copper and tin it is at present preferred that the plating consist of copper and 10% tin, although the percentages of copper and tin may be varied Within the limits of composition of known bronzes.

The thickness of the electrodeposit of copper and zinc or tin may vary considerably. Very satisfactory results have been obtained with platings of about .0005 in thickness. Platings as thin as .0002" have been treated in accordance with the invention. Regardless of the thickness of the codeposit of copper and the zinc or tin the treated product is greatly superior in resistance to corrosion as compared to similar products Without the treatment. Platings much thicker than .0005" may be treated as described. From the commercial standpoint it is desirable to use the least possible thickness that will provide the desired results as regards resistance to corrosion.

The metal surface after being electroplated with the codeposit of copper and zinc or tin of desired thickness is then heated to elevated temperature preferably somewhat above the melting point of the zinc or tin, and maintained at the elevated temperature for a time interval sufiicient to provide the desired corrosion-resistant coating. Times of about ten minutes to half an hour or even more may be used. In general the higher the temperature the less the heating time, and

tion. Other neutral and reducing atmospheres may be employed in place of nitrogen atmospheres. Instead of a non-oxidizing atmosphere in the furnace, a plating of a metal such as chromium may be applied to the surface of the codeposited plating of copper and the low melting point constituent in order to protect the same from oxidization during heat treatment. At the.

end of heating period the parts are allowed to cool. They may be removed from the furnace and air cooled or they may be quickly cooled as by quenching in water.

Any metallic surface having a melting point higher than the temperature to which the codeposited coating of copper and the low melting point metal is heated and on which the copper and low melting point metal may be simultaneously electroplated, may be utilized as the base metal. Since temperatures somewhat above the melting pointof zinc or tin preferably are employed in the heat treatment, the composition of the base metal must have in any particular application a melting point sufl'iciently high to permit this. Thus the codeposit of copper and tin may be applied to such materials as zinc base die castings having a comparatively low melting point and thereafter heat treated at a temperature above the melting point of tin without danger of melting the die casting, whereas the codeposit containing zinc could not be heat treated above the melting point of zinc without melting the zinc base die casting. 7

Very satisfactory corrosion-resistant surfaces have been obtained by codepositing copper and zinc or copper and tin to a thickness of .0005" directly on a cleaned steel surface and thereafter heat treating the surface and plating at a ,tem-

perature slightly above the melting point of the zinc or tin. Still better results as regards resistance to corrosion are obtained by first plating the steel surface with a thin deposit of copper and following this by a codeposit of copper and a metal such as zinc or tin and then heat treating the same. Copper platings of from .0001 to .001" have been employed, progressively better results being obtained with platings up to about .0005 in thickness.

Any suitable plating bath may be employed in the simultaneous eleotrodeposition of the copper and the lower melting metal such as zinc and tin. Electrolytes for codepositing copper and zinc and copper and tin are known and need not be described specifically herein. As a representative type of solution that has been used the cyanide may be mentioned. It is desirable that the parts be thoroughly cleaned prior to plating.

The following examples of specific procedure may be given as illustrative:

Example 1.-A cold rolled steel panel 3" x 6" was. plated with a brass electrodeposit about .0002" in thickness consisting of approximately 30% zinc and the balance copper and was thereafter placed in a nitrogen atmosphere furnace maintained at a temperature of 950 F. and allowed to remain in the furnace for fifteen minutes. The heated panel and coating thereon was then removed from the furnace and quenched quickly in water.

Example 2.-Same as Example 1 except that the brass electrodeposit was .0005" in thickness. Example 3.-Same as Example 1 except that a furnace temperature of 800 F. was used and the plated panel was allowed to remain in the furnace for a total of twenty-five minutes.

Example 4.Same as Example 3, except'that the brass electrodeposit was .0005" in thickness. Example. 5.A steel shell casing about 10 inches long and about 2" in diameter was plated with a brass electrodeposit .0005" in thickness consisting of approximately 30% 'zinc and the balance copper and was thereafter heated in a furnace at a temperature of 815 F. A time of fifteen minutes was allowed to attain temperature and thereafter the casing was heated for a time of thirty minutes at 815 F.

Example 6.Same as Example 5except that a copper electrodeposit .0005" in thickness first was applied to the steel shell casing and the brass electrodeposited on the copper electrodeposit.

Ea ample 7.-Same as Example 5 except that a thin flash coating of chromium was applied to the brass electrodeposit prior to heat treatment.

Example,8.A cold rolled steel panel was plated with a bronze electrodeposit of about .0005" in thickness consisting of about 10% tin and. the balance copper and was heated in a furnace at a temperature of 475 F. A time of ten minutes was allowed to bring the panel and bronze electrodeposit to temperature and thereafter the plated panel was maintained at 475 F. for thirty minutes.

Example 9.Same as Example 8 except that an electrodeposit of copper of about .0005" was applied first to the steel panel and the. bronze electrodeposited on the copper.

Example 10.Same as Example 8 except that a temperature of 650 F. was employed.

Various changesand modifications of the embodiments of my invention described herein may be made without departing from the principles of my invention.-

I claim:

The method of formin a corrosion-resistant surface on a ferrous metal surface which includes, electrodeposlting a layer of copper of about .0001 to .0005" in thickness onto the ferrous metal layer, applying to the electrodeposited layer of copper a coating .0002" to .0005 in thickness composed of about copper and 30% zinc by simultaneously electrodepositing the copper and zinc in the given percentages onto the electrodepositedcopper layer, applying a coating of chromium to the copper-zinc coating, and thereafter heating the ferrous metal, electrodeposited copper layer, electrodeposited copper-zinc coating and chromium coating at a temperature of about 800 F. to 950 F. for a time ranging from ten to about thirty minutes.

GEORGE: W. KELLOGG.

REFERENCES CITED The following references are of record in the file of this patent:

' UNITED STATES PATENTS 

